An ID saw slicing machine is a slicing machine equipped with a thin doughnut-shaped blade with the inner edge coated with a hard material such as diamond powder. This machine is particularly useful in slicing a brittle rod such as a single crystal semiconductor ingot. As the blade of the ID saw slicing machine is rotated at a high speed, either the ingot or the slicing machine is slid in a manner such that the inner edge of the doughnut-shaped blade crosses the ingot in a direction normal to the axis of the ingot.
In the technical field of semiconductor wafer manufacturing, a silicon single crystal pulled up in a conventional single crystal pulling apparatus is sliced with an ID saw slicing machine (hereinafter also referred to as "an ID slicer") in a direction normal to the axis of the ingot, and a number of thin silicon semiconductor wafers are cut out. However, after a long use, the diamond-powdered grinder edge of the blade of the ID slicer wears and is covered with a densified cut powder layer and thereby starts wobbling roughly; this causes a sliced wafer to have a so-called bow to a greater degree, which is a warp of the wafer in one direction. The bow is attributable to the residual stress in the wafer.
In order to solve this problem, some of the commercially available ID slicers are equipped with a displacement gauge which measures the wobble displacement of the blade of the slicer. The wobbling amount of the blade is detected by means of the displacement gauge, and based on the result of the detection, the blade is appropriately dressed and trued; also the feed rate of the ingot is modified in response to the result of the detection of the blade displacement in a feed back manner. Thus, efforts have been made in an attempt to obtain semiconductor wafers having as small a bow as possible.
However, in the conventional slicing method and apparatus, when the single crystal ingot to be sliced has a large diameter, as the current trend makes this situation more common, the inner diameter of the ID slicer has to be likewise increased, and the greater the inner diameter of the ID slicer, the harder it is to minimize the bow of the semiconductor wafer, since the greater inner diameter of the ID slicer results in greater wobbling of the slicer blade.
Also, since the wobble displacement of the blade is by nature very small in magnitude, it is a difficult task to control and remove the bow of the semiconductor wafer through a feed back manner based on the wobble displacement measurement. Therefore, a need continues to exist for an improved method and apparatus that can reduce even the infinitesimal bow from the wafers.
The present invention was made in view of these problems, and it is an object of the invention to provide a method of using an ID slicer for slicing a single crystal ingot into wafers in which the amount of bow is reduced, and also to provide a slicing apparatus for effecting this method.